The invention relates in general to compressor control, and more particularly to the prevention of the consequences of "surging" in such compressor control. "Surging" is a phenomenon caused by the compressor operating below a given amount of horse power or gas volume and the resulting occurrence of nonsteady state condition compounded by erratic control and an uncontrolled output.
The problem of surging and the prevention thereof have been explained in "Centrifugal and Axial Compressor Control by Gregory K. McMillan (The Instrument Society of America, 67 Alexander Drive, P.O. Box 12277, Research Triangle Park, NC 27709), 1983.
The present invention aims at an early detection of the occurrence of a surge, thereby providing an immediate opportunity of preventing the consequence thereof. Therefore, the invention distinguishes itself from the prior art methods by preventing the consequences of a surge by the timely and accurate detection of an occurring surge.
The invention is based on the magnitude of the current of the motor driving the compressor at the critical moment. The prior art has recognized the relationship existing between the volume of the compressed gas, or the pressure of the compressor, to the energy of the motor in operation, or its current. However, the object, there, has been to control the compressor as a function of the sensed current in order to prevent a surge, not to detect the imminence of a surge, or in order to control the compressor in relation to the gas volume while observing the surge limit. See, for instance, U.S. Pat. Nos. 3,778,695; 4,519,748 and 3,380,650, and also: "Surge Control For Multistage Centrifugal Compressors" by David F. Baker in Chemical Engineering May 31, 1982, pp. 117-122; "Improved Surge Control for Centrifugal Compressors" by N. Staroselsky and L. Ladin in Chemical Engineering May 21, 1979, pp. 175-184; and "Surge Control for Centrifugal Compressors" in Chemical Engineering Dec. 25, 1972, pp. 54-62.